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Chapter 5 The Filesystem

Chapter 5 The Filesystem. Outline. File System Architecture Pathname File Tree Mounting File Types inode and file Link File Access Mode Changing File Owner FreeBSD bonus flags. File System Architecture (1). Application  Kernel  Hardware

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Chapter 5 The Filesystem

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  1. Chapter 5The Filesystem

  2. Outline • File System Architecture • Pathname • File Tree • Mounting • File Types • inode and file • Link • File Access Mode • Changing File Owner • FreeBSD bonus flags

  3. File System Architecture (1) • Application  Kernel  Hardware • Applications call system-calls to request service • Kernel invokes corresponding drivers to fulfill this service

  4. File System Architecture (2) • The basic purpose of filesystem • Represent and organize the system’s storage • Four main components: • Namespace • A way of naming things and arranging them in a hierarchy • API • A set of system calls for navigating and manipulating nodes • Security model • A scheme for protecting, hiding and sharing things • Implementation • Code that ties the logical model to an actual disk

  5. File System Architecture (3) • Objects in the filesystem: • What you can find in a filesystem: • Files and directories • Hardware device files • Processes information • Interprocess communication channel • Shared memory segments • We can use common filesystem interface to access such “object” • open、read、write、close、seek、ioctl…

  6. pathname • Two kinds of path • Absolute path  start from / • Such as /u/gcp/92/9217810/test/hehe.c • Relative path  start from your current directory • Such as test/hehe.c • Constrains of pathname • Single component: ≦ 255 characters • Single absolute path: ≦ 1023 characters

  7. File Tree (1)

  8. File Tree (2) • standard directories and their contents

  9. Mounting file system (1) • The filesystem in composed of chunks • Most are disk partitions • Network file servers • Memory disk emulators • Kernel components • Etc,… • “mount” command • Map the mount point of the existing file tree to the root of the newly attached filesystem • % mount /dev/ad2s1e /home2 • The previous contents of the mount point become inaccessible

  10. Mounting file system (2) • Example

  11. Mounting file system (3) • Filesystem table – fstab • Automatically mounted at boot time • /etc/fstab • Filesystem in this file will be checked and mounted automatically at boot time Ex. bsd1’s /etc/fstab # Device Mountpoint FStype Options Dump Pass# /dev/ad0s1b none swap sw 0 0 /dev/ad0s1a / ufs rw 1 1 /dev/ad0s1e /backup ufs rw 2 2 /dev/ad0s1d /home ufs rw 2 2 /dev/acd0 /cdrom cd9660 ro,noauto 0 0 csduty:/bsdhome /bsdhome nfs rw,noauto 0 0

  12. Mounting file system (4) • Unmounting File Stsyem • “umount” command • % umount node | device • Ex: umount /home, umount /dev/ad0s1e • Busy filesystem • Someone’s current directory is there or there is opened file • Use “umount –f” • We can use “lsof” or “fstat” like utilities to figure out who makes it busy

  13. Mounting file system (5) • lsof, fuser and fstat commands • lsof (/usr/ports/sysutils/lsof) –list open files • fuser (/usr/ports/sysutils/fuser) –list IDs of all processes that have one or more files open • fstat (FreeBSD) % lsof /home/chwong COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME lsof 27097 root cwd VDIR 0,75 512 730114 /home/chwong lsof 27098 root cwd VDIR 0,75 512 730114 /home/chwong tcsh 44998 chwong cwd VDIR 0,75 512 730114 /home/chwong sh 55546 mysql cwd VDIR 0,75 512 730114 /home/chwong tcsh 99025 chwong cwd VDIR 0,75 512 730114 /home/chwong % fuser /home/chwong /home/chwong: 55546c 44998c 99025c 27169c % fstat /home/chwong USER CMD PID FD MOUNT INUM MODE SZ|DV R/W NAME chwong fstat 27101 wd / 730114 drwxr-xr-x 512 r /home/chwong chwong tcsh 99025 wd / 730114 drwxr-xr-x 512 r /home/chwong chwong tcsh 44998 wd / 730114 drwxr-xr-x 512 r /home/chwong mysql sh 55546 wd / 730114 drwxr-xr-x 512 r /home/chwong

  14. File Types (1) • File types • Regular files • Directories • Include “.” and “..” • Character and Block device files • UNIX domain sockets • Named pipes • Symbolic links

  15. drivers major capabilities 1 2 … Major =5 Minor = 0 5 open,read,write,… … File Types (2) • character and block device files • Use “mknod” to build special file • % mknod name [c|b] major minor • The same major number will use the same driver

  16. File Types (3) • UNIX domain socket • Created by socket() • Local to a particular host • Be referenced through a filesystem object rather than a network port

  17. File Types (4) • Named Pipes • Let two processes do “FIFO” communication

  18. File Types (5) • Symbolic Link • A file which points to another pathname • % ln –s ori-file soft-file • Like “short-cut” in Windows

  19. File Types (6) • File type encoding used by ls chwong@chbsd:/var/run> ls -al total 36 drwxr-xr-x 6 root wheel 512 Oct 2 23:32 . drwxr-xr-x 22 root wheel 512 Oct 1 05:00 .. srw-rw-rw- 1 root wheel 0 Sep 30 21:00 log

  20. inode and file (1) • inode • A structure that records information of a file • You can use “ls –il” to see each file’s inode number

  21. inode and file (2) • Filesystem • Boot blocks • Super block • Inode list • Data block

  22. inode and file (3) • More detail of inode and data block

  23. testdir chwong /home/chwong/testdir inode and file (4) • Example • . • .. • testdir

  24. Hard Link V.S. Symbolic Link (1) • Link • Hard link • associate two or more filenames with the same inode • % ln ori-file hard-file • Soft (symbolic) link • A file which points to another pathname • % ln –s ori-file soft-file

  25. Hard Link V.S. Symbolic Link (2) % touch index % ln index hlink % ln –s index slink

  26. File Access Mode (1) • rwxr-xr-x • User, group, other privileges • chmod command • % chmodaccess-stringfile • % chmod u+x test.sh • % chmod go-w .tcshrc • % chmod u+w,r-w hehe haha • % chmod –R 755 public_html/

  27. File Access Mode (2) • setuid, setgid, sticky bit • setuid, setgid on file • The effective uid/gid of resulting process will be set to the UID/GID of the file • setuid • passwd, chsh, crontab • setgid • top, fstat, write • setgid on directory • Cause newly created files within the directory to be the same group as directory • sticky on directory • Do not allow to delete or rename a file unless you are • The owner of the file • The owner of the directory • root

  28. File Access Mode (3) • Decimal argument of chmod • setuid: 4000 • setgid: 2000 • stiky : 1000

  29. File Access Mode (4) • Assign default permissions: umask • Shell built-in command • Inference the default permissions given to the files newly created. • The newly created file permission: • Use full permission bit (file: 666, dir: 777)xorumask value. • Example:

  30. Changing File Owner • Changing File Owner • Commands: • chown -- change user owner • chgrp -- change group owner • Change the file ownership and group ownership • % chown –R chwong /home/chwong • % chgrp –R cs /home/chwong • % chown –R chown:cs /home/chwong

  31. FreeBSD bonus flags • chflags command • schg system immutable flag (root only) • sunlnk system undeletable flag (root only) • sappnd system append-only flag (root only) • uappend user append-only flag (root, user) • uunlnk user undeletable flag (root, user) • … chbsd [/home/chwong/test] -chwong- touch file chbsd [/home/chwong/test] -chwong- ls -lo -rw-r--r-- 1 chwong user - 0 Oct 3 18:23 file chbsd [/home/chwong/test] -chwong- chflags uunlnk file chbsd [/home/chwong/test] -chwong- ls -lo -rw-r--r-- 1 chwong user uunlnk 0 Oct 3 18:23 file chbsd [/home/chwong/test] -chwong- rm -f file rm: file: Operation not permitted chbsd [/home/chwong/test] -chwong- sudo rm -f file rm: file: Operation not permitted chbsd [/home/chwong/test] -chwong- chflags nouunlnk file chbsd [/home/chwong/test] -chwong- rm -f file chbsd [/home/chwong/test] -chwong-

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